Speed and acceleration responsive device



July 9, 1946. R. N. LESNICK SPEED AND ACCELERATION RESPONSIVE DEVICE Filed July 1, 1942 Gttomeg L m 0 mm Mn ow 6 MM 8 J L A N 0 r h Z12: I m@ mfi/ #1 m 5 mm. 9 2 HM 8 A no 1 9 d z 1 7 z 3 5 F O 0 a w J 1 P. 5 w m d m y 0 M P 31 7 w v M W u 0 Patented July 9, 1946 SPEED AND ACCELERATION RESPONSIVE DEVICE Robert N. Lesnick, Camden, N. 1., ass'lgnor to Radio Corporation of America, a corporation oi" Delaware Application July 1, 1942, Serial No. 449,231

3 Claims. (Cl. 172-239) This invention relates to speed and acceleration responsive devices and more particularly to systems for producing displacement or operation of acontrcl device in response to-the speed or acceleration, or both, of a rotating shaft.

Speed and acceleration responsive devices of this type iind application in servo systems or follow-up systems such as are used to move a relatively massive object in accordance withthe motion of a relatively small control device, In certain cases, it is desirable to add to the-elfect of the control device an auxiliary factor which i a function of the speed or acceleration of the driven object, in order to compensate lag or hunting of the driven object with respect to the control device.

Accordingly it is an object of this invention to provide an improved method of and means for deriving a displacement component related in magnitude and direction to the angular. velocity or acceleration, or both, of a rotatable shaft.

It is a. further object to provide an improved means for correcting the errors inherent in certain types of servo systems.

These and other and incidental objects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawing, in which Fig. 1 is a side elevation, partly in section, of a speed and acceleration responsive device constructedaccording to the invention, Fig. 2 is a view through the section 2-2 of Fig. 1, Fig. 3 show a modified speed-responsive means, and Fig. 4 is a schematic diagram of a servo system embodying the invention.

Referring to Fig. l, a shaft I is driven at any predetermined angular velocity and acceleration by a device 3, which may be an electric motor, in accordance with the operation of controlling means associated with said device. The shaft 1 may be connected with a mechanical load generally designated by the block ll in the drawing. The shaft 1 is also connected to a gear I of a differential 9. A corresponding gear H at the other side of the diiferentlal i is connected through a shaft II to a control device (not shown) which responds to movement of the shaft l3 under the forces of springs l and inertia til not exactly alike, or vary dificrently with temperature or age, the springs it and maybe arranged to bear against stops 22 on the supporting member 2i. The spring arrangement illustrated will accommodate angular displacements oi the shalt it of approximately ten degrees in either direction from the position or static equllibrium. If lawn-displacements are required, a modified spring structure or suitable gearing may be employed. v M

The orbit sears 23 oi the differential 8 are rotatably mounted on radially, extending shafts 25 which are secured to a ring 21. The ring 21- may be of relatively massive construction in order to function as a fly wheel or inertia load, as hereinaiter described. Radlalvanes 29 may be provided on the surface of the ring l! to provide a frictional load on the system by air drag, or by similar action in any suitable'fluld in which the device may be immersed. The vanes 28 may be omitted and sliding friction means substituted, such as brake shoes 42 bearingin the ring forces of the means 2! and 29 to control the 9.9-

plicatlon of power to the motor I. A radial arm i7 is secured to the shaft 13 and extends between two springs ll and 20 fastened on a fixed support 2| (Fig. 2). In order to determine positively the equilibrium position of the arm l'l, even if the characteristics of the two spring; are

21, as illustrated in Fig. 3. Another alternative is to provide the ring 21 with a radial flange of conductive material, and produce an eddy current drug related to the speed by means of magnets, as in the well known watt-hour meter construction. The operation of the device is as follows; Rotation of shaft l imparts to the gear I an equal motion which is divided bywell known diflerentlal action between the shaft l3 and the ring 21 inversely as they tend to. oppose' motion. The motion of the shaft I2 is opposed by one of the springs Ii and 20, and that of the rind 21 is opposed by the inertia force of the ring and the frictional force against the vanes 28. The spring force is a vfunction of the angular displacement of the shaft II, and the inertia and frictional forces on the ring 21 are functions respectively of the angular acceleration and angular velocity of the ring. Thus the device functions as a yield-.

able coupling between the shaft; 1 and I3 with components responsive to the acceleration and to the velocity of the shaft] to rotate the shaft l2 against the spring restraining force.

The shaft M will be rotated to an angular position in which the spring force balances the inertia and frictional torces on the ring 21. Hence the position of the shaft 13, and the control device ls related'to the annular acceleration and the'angular velocity of the shaft l. The exact relations are determined by the moment of lnertla of the ring 21, the area and arrangement of the vanes 20 or other frictional means. and the block 4:.

3 constants of the springs I9 and :0. These factors are all to be considered in the design of the system for any specific application.

Referring to Fig. 4, an electrical servo system embodying the invention is illustrated. A pair of Belsyn type transformers 30 and ii are mechanically connected to a control shaft 31 and a wntrolled shaft IM respectively. The shaft :3 is arranged to be rotated by any desired means such as a manually operable crank 35. The shaft III is connected to a driving motor I03 and to a device 31 like the mechanism illustrated in Figs. 1 and 2 of the drawing. The mechanical load to be operated is represented by the block I05, also connected to the driving motor W3.

A Selsyn transformer H5, similar to transformers l and 3|, is electrically connected between corresponding windings of said transformera; the rotor, for example, of the transformer [l5 being connected to the stator of the transformer I0 and the stator of the transformer i ii being connected to the stator of the transformer II. The stator of the transformer H5 is maintained stationary, and the rotor is connected through a shaft llll, corresponding to the shaft it of Fig. 1, to the device 31.

The rotor winding of the transformer 3| is energized with alternating current from supply lines 88. The rotor of the transformer 30 is connected to the signal input circuit of an amplifier and motor control device designated by the The device if is also energized from the lines 38, and is arranged to control the motor in accordance with the amplitude of the control input voltage and its polarity with respect to a voltage derived from the supply lines 89.

The operation of the system of Fig. i is as follows. The output voltage of the transformer to is amplified in the device 4!. If said voltage is zero, the motor I0! is not energized. If the voltuse is not zero, the motor His is caused to rotate and turn the rotor of the transformer 3i, changing the voltages applied to the transformer H5 and through it the voltages at the primary of the transformer 30. The voltage at the secondary of the transformer it depends on both the voltages impressed upon its primary, and the physical position of its rotor with respect to its stator. Thus the voltage at the input of the device 4| changes with the rotation of the motor I03 until it is again zero, whereupon the motor I03 stops and the system remains at rest until unbalanced by some outside force such as rotr Z'Jh of the crank 35.

In nearly all systems of this class, certain errors are inherent. For example, a consideration of the principles of operation shows that there must be some difference in the angular positions of the controlling and driven shafts in order to provide a difference in the two voltages compared in the device H and operate the motor. Hence the two shafts normally do not remain .in positional agreement while the system is in motion. Another and often troublesome effect is that of "hunting, oroverrunning and reversal of the driven member about the point of positional agreement with the control shaft. Servo systems of many types, as well as electrical systems, are subject to such difficulties.

It has been found that the above described defects may be partially or substantially eliminated by adding to the control signal or equivalent force a quantity related in magnitude to the velocity and acceleration of the driven member. In the system illustrated in Fig. 3 this is done by displacing the rotor of the transformer H5 by means of the device of Fig. 1 described above. For example with the system initially at rest the crank 35 is rotated through some predetermined angle. Voltage applied to the transformer II from the A.-C. lines 39 is converted to three separate in-phase voltages which are applied to the stator of the transformer H5. The amplitudes of these voltages with respect to each other depend upon the angular position of the rotor of the transformer 3i. Corresponding voltages are produced in the stator of the transformer I I5 and as long as the rotor remains in its initial position with respect to the stator thereof, the output of the transformer I I5 corresponds exactly to the output of the transformer 31 This output is applied to the stator of the transformer 30, providing a resultant field through the armature thereof and inducing a voltage in the rotor winding which corresponds in amplitude to the difference in the angular positions of the crank 35 and the output shaft IIH. This voltage is amplified by the amplifier ll, causing the motor I03 to rotate toward a position corresponding to that of the crank 35.

As' soon as the motor I03 starts to rotate, the input shaft of the device 31 is rotated, causing the output shaft to rotate in the opposite direction due to inertia and friction loading on the differential spider member. This causes the rotor of the transformer H5 to move through an angle which is a predetermined function of the acceleration and velocity of the driving motor I03, altering the relationship between the three voltages in the output circuit of the transformer and hence advancing the angular position of the field in the transformer 30 ina direction opposite to the direction of rotation of the crank 35. This increases the magnitude of the control signal applied to the amplifier 4i, providing more energization of the motor Hi3 and hence a greater torque than would normally be produced as a result of the difference in angular position between the crank and the driving motor. Thus upon starting, the inertia of the load is overcome by increasing the total control signal in response to the acceleration of the output shaft. If rotation of the crank 35 is continued, the output shaft will rapidly assume the velocity of rotation of the crank and as soon as acceleration ceases the rotor of the transformer I [5 will tend to assume its initial position under the action of the springs l9 and 20. However the frictional load on the device 31 will continue to provide its original effect, maintaining an advance in the position of the field in the transformer 30 proportional to the velocity of the shaft IOI. Thus the mag nitude of the control signal is higher at the higher velocities of operation, although not directly proportional to either the displacement or the velocity. Upon retardation of the crank 35 the inertia of the device 31 acts in the opposite direction from that during acceleration, reducing the resultant control signal applied to the amplifier M to a value which is less than the normal displacement proportional signal, tending to reduce the energization of the motor more rapidly than the difference between the positions of the crank 35 and the output shaft Jill is reduced. At the same time the frictional load on the device 31 tends to maintain the control signal at a higher level in response to the velocity of rotation of the shaft ID]. This component retains its original sense although the acceleration component is reversed. Thus as the output shaft tends to drag or frictionforces, resulting in a displacement of the output shaft which is a function of the velocity and acceleration of the input shaft. An illustrative application of this device in an electrical servo system has also been described.

I claim as my invention:

1. In a servo system including a control shaft, a controlled shaft, means for comparing the angular positions of said shafts, means for deriving a force related to the difference in said positions and applying said force to said controlled shaft so as to drive said controlled shaft toward a position corresponding to that of the control shaft, means for deriving auxiliary forces related in magnitude and direction to the velocity and to the acceleration of said controlled shaft comprising differential means connected to said controlled shaft and connected to drive a mechanical load comprising inertia and friction elements against a resilient restraining member, and means for deriving said auxiliary forces in response to the displacement of said restraining member.

2. In a servo system comprising a control shaft.

a driven shaft, means responsive to the differ ence in the angular positions of said shafts to control a motor to drive said driven sliaf t toward positional agreement with said control shaft, means responsive to the angularvclocity and acceleration of said driven shaft to produce an auxiliary control effect on said motor. including a differential connected between said driven shaft and an auxiliary control shaft resiliently restrained against rotation, anda mechanical load connected to said differential to control the transmission of-torque from said driven shaft through said differential to said auxiliary control shaft.

3. In a servo system including a driven shaft, a motor coupled to said shaft, and means for energizing said motor in response to a control input signal, angular displacement responsive means for producing an auxiliary signal in addition to said control input signal, differential gearing including two shafts and a spider member,

said shafts being connected respectively to said driven shaft and to said displacement responsive means, and a mechanical load comprising friction and inertia elements coupled to said differential spider member to cause rotation of said displacement responsive means as the sum of predetermined functions of the speed and the acceleration of said driven shaft.

ROBERT N. LESNICK. 

